1. Field of the Invention
The present invention relates to a recording sheet for use in an OHP in such a manner that a toner image is transferred/fixed to the surface of a film.
2. Related Art Statement
A conventional wet-type copying machine employs a copying method arranged in such a manner that a liquid developer is used to perform developing, a toner image is transferred to the surface of a film and a heat source is brought into direct contact with the surface of the film to which the toner image has been transferred so that the above-described toner image is fixed. Therefore, there arises a problem of an abnormal phenomenon such as undesirable run of the image or the like because the ordinary OHP sheet for use in a conventional dry-type copying machine cannot satisfactorily absorb the solvent contained in the liquid developer.
In order to overcome a problem of the type described above, there have been made a variety of disclosures.
That is, a technology has been disclosed in Japanese Patent Laid-Open No. 1-302266 which is arranged in such a manner that the surface of the sheet is subjected to a roughening treatment by using a hydrophobic resin and thereby the above-described solvent can be absorbed by the roughened surface layer of the sheet so that the image can be fixed satisfactorily. According to this method, no problem arises in a case where the quantity of the toner to be transferred is a small quantity. However, if a large quantity of the toner must be transferred, the above-described problem of the run of the image cannot be overcome because the roughened surface layer cannot satisfactorily absorb the above-described solvent. Another technology has been disclosed in Japanese Patent Laid-Open No. 2-47667 which is arranged in such a manner that a porous surface layer made of a devitrified resin is formed on the surface of the sheet to cause the toner to be perfectly absorbed by the porous surface layer regardless of the quantity of the toner. Furthermore, the sheet is passed through heating rollers so that the porous surface layer is melted and the devitrified porous surface layer is returned to the transparent state. As a result, the image is fixed as desired. Although the generation of the run of the image can be prevented according to the above-described method, excessively large thermal energy is required to melt the resin such that the temperature of the heating rollers must be raised to a level which is, by 20.degree. C. to 30.degree. C., higher than the temperature which is required to fix an image to an ordinary sheet.
On the other hand, the copying method employed in a conventional electrostatic dry-type copying machine is a method in which a toner image is formed by simply copying and printing an image to the surface of a recording sheet. The conventional recording sheets are exemplified by a recording sheet made of a non-porous type transparent plastic film subjected to a surface treatment such as a charge prevention process and a recording sheet made of a plastic film having the surface subjected to a roughening treatment in order to improve the toner fixing facility.
However, in a case where an image is copied and printed to the above-described recording sheet by the electrostatic dry-type copying machine, there arises a problem in that the toner can easily be separated from the sheet if the formed toner image is scrubbed by the claw or the like or the sheet is bent or crumpled because the formed toner image is baked and fixed to the surface of the sheet by only the binder contained in the toner ink.